OBD Transmission Temp Devices?

[tacorancher]

If you're in Houston, you could well be like my observation when our summer weeks stayed hot and warm in the evenings. The dashboard display showed temperature way before other times of the year.

Overall this is not something I worry about. My pickup has been task and work oriented. I just did summer conditions towing 5000 pounds over about 240 miles of climbs, some poor roads, and some bits unpaved. The temp gauges and all were fine when there was a lot of boost, and low MPG. It was February, but I spent a month and 3000 miles in CO pass climbing and back country sports access without problems.

I also don't get the worries many have when I consider the competition and realities of choice. My situation needed a minimum 6 ft bed pickup. The competition is full of known transmission problems. The Tacoma really only has the early run TSB as a problem and not yet any broad recalls, and a lot seem daft to the matter of how the Tacoma outsells its direct competition. Of course some Tacoma problems have to be out there when their sales kill it against Rangers, GM and Nissan.

Yeah. Not concerned. 19,000 miles zero issues.

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[TrustButVerify]

From some generic AI searching it seems that as long as the transmission fluid temp is below 225 it should be fine. I do wonder if the high temps might shorten the fluid life or if there is a good way to tell when it really needs changed.

The on board computer tracks a function called ATF thermal degradation. I do not know how to access the value or reset the value without using TechStream. It's an oil life monitor for the ATF. If it reaches a value of 50,000, the fluid is due for a change. I do not have techstream. This is referenced in the service manual on the section of ATF fluid changes.

If you are going off pavement (off road more than snow or flat ground), and there's significant elevation changes or high transmission loads, you'll see trans fluid temps skyrocket. The middle point of the gauge on the dash is something like 180-215F. At 215 to 220, the gauge will rapidly climb towards the redline around 250F+. This happens relatively quickly if you are going up and down hills and ravines and switchbacks. Going downhill in low gear (not 4LO) will also put a lot of heat into the transmission. I monitor realtime transmission temps using a temp gauge showing actual temp in F.

The only options you have in these situations are to either drop out of 4WD back into 2WD to let it cool down, or moving to 4LO. Speed is limited in 4LO to about 20mph, ideally slower since it's really screaming at 4000RPM.

What you gain from lower trans temps in 4LO you lose in higher engine oil temps, which will start to climb rapidly as well. If you are running 0w-20, you'll be exceeding what is responsible temps for that viscosity when oil temps are north of 240F. The oil film breaks down just at the time when the engine is at high RPM and high load with these high temps. And if you are using TGMO 0w-20, which is jacked with viscosity improvers, it's not good for oil longevity.

The cooling abilities at lower speeds are somewhat anemic. If it's hot, and you're at elevation and using a lot of boost, both the engine oil and the transmission heat up and remain hot for a long time. I've had to run the cab heat at full blast to keep water temps down and thus helping keep oil temps lower, while running in 4lo in the mountains on more technical tracks. I don't think the engine uses any boost at all in 4LO which is good, IMO.

Summary:
Mountain climbs up BLM and USFS type roads in 4HI make trans temps jump up.
Using 4LO mitigates this, but causes engine oil temps to increase.
0W-20 oils are poorly suited to high load high temps. Perhaps 0W-30 or 0W-40 for heavy off road use especially at high ambient temps or with heavier loads.
Careful monitoring of ATF temp and oil temps is important for longevity. It helps the driver have a bit of mechanical sympathy long before the dash gauge surprise you with an overheat warning.

 

[izzy]

The on board computer tracks a function called ATF thermal degradation. I do not know how to access the value or reset the value without using TechStream. It's an oil life monitor for the ATF. If it reaches a value of 50,000, the fluid is due for a change. I do not have techstream. This is referenced in the service manual on the section of ATF fluid changes.

If you are going off pavement (off road more than snow or flat ground), and there's significant elevation changes or high transmission loads, you'll see trans fluid temps skyrocket. The middle point of the gauge on the dash is something like 180-215F. At 215 to 220, the gauge will rapidly climb towards the redline around 250F+. This happens relatively quickly if you are going up and down hills and ravines and switchbacks. Going downhill in low gear (not 4LO) will also put a lot of heat into the transmission. I monitor realtime transmission temps using a temp gauge showing actual temp in F.

The only options you have in these situations are to either drop out of 4WD back into 2WD to let it cool down, or moving to 4LO. Speed is limited in 4LO to about 20mph, ideally slower since it's really screaming at 4000RPM.

What you gain from lower trans temps in 4LO you lose in higher engine oil temps, which will start to climb rapidly as well. If you are running 0w-20, you'll be exceeding what is responsible temps for that viscosity when oil temps are north of 240F. The oil film breaks down just at the time when the engine is at high RPM and high load with these high temps. And if you are using TGMO 0w-20, which is jacked with viscosity improvers, it's not good for oil longevity.

The cooling abilities at lower speeds are somewhat anemic. If it's hot, and you're at elevation and using a lot of boost, both the engine oil and the transmission heat up and remain hot for a long time. I've had to run the cab heat at full blast to keep water temps down and thus helping keep oil temps lower, while running in 4lo in the mountains on more technical tracks. I don't think the engine uses any boost at all in 4LO which is good, IMO.

Summary:
Mountain climbs up BLM and USFS type roads in 4HI make trans temps jump up.
Using 4LO mitigates this, but causes engine oil temps to increase.
0W-20 oils are poorly suited to high load high temps. Perhaps 0W-30 or 0W-40 for heavy off road use especially at high ambient temps or with heavier loads.
Careful monitoring of ATF temp and oil temps is important for longevity. It helps the driver have a bit of mechanical sympathy long before the dash gauge surprise you with an overheat warning.

Exactly what I've seen after offroading with my Scan Gauge, but even during a 10mi 5600ft climb in 4Lo, nothing overheated. Ambient was close to 90F, engine oil was around 230, trans fluid around 230 as well locked into 4Lo.

I'm doing 5000 mile OCI, and I'll be changing the trans fluid every 25k.

Should be enough to make the trans last a while.

 

[TacoFreak]

@TrustButVerify Thanks, that is interesting information. I wonder if dealers ever use TechStream to check ATF condition or if they only check if there is a complaint.

 

[TrustButVerify]

@TrustButVerify Thanks, that is interesting information. I wonder if dealers ever use TechStream to check ATF condition or if they only check if there is a complaint.

They're supposed to reset it if the fluid gets changed. So I suppose if you went in and had the transmission serviced at the dealer they would do this. I can't imagine they would ever bother checking it unless there was an issue.

Toyota does a lot of interesting things in warranty and out of warranty. If it was a warranty related thing they probably would be more diligent about resetting it and worrying about it. They use a higher quality of parts when they do warranty work then when they do service work.

I'll give you an example, air filters. There's two part numbers for air filters. There's a $15 air filter and a $20 air filter. The $20 air filter is thicker than the $15 air filter. But if you're just in for a routine service and you're having the dealer change the air filter, they will use the cheap one. But if it's warranty work Toyota requires them to use the expensive one. There's also cheaper brake pads and more expensive brake pads. And even though you can't buy it, the oil filter that comes on the truck is a different grade of oil filter than the one that you buy over-the-counter. Both are OEM parts, one is just made in Japan and the other one made in whatever low bid factory Toyota has contracted with.

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